The present invention relates to low cost, acid-resistant, high early strength hydrothermally cured pozzolanic cement compositions, preferably ones that are also lightweight, which are capable of being used after being admixed with water to form building floors, walls, and the like and also processed into building materials such as brick, cinder block, roofing and flooring tile, monolithic slabs, concrete pipe, utility poles, and the like from essentially indigenous industrial and/or biogeneric waste by-products.
In many areas of the United States and more often in other areas of the world such as third-world countries, it is difficult to find low-cost, lightweight, high strength building materials which are fire resistant, environmentally stable, and which have structural integrity so as to provide sturdy and affordable living units.
There is also the concomittant problem of ecologically sound disposal of industrial and agricultural by-product waste materials. These include kiln dust, fly ashes; biogeneric wastes, such as bagasse ash, rice hull ash, and other siliceous materials such as fume silica, a by-product resulting from the production of silicon and zircon.
There have been numerous efforts in the past to utilize large percentages of such materials in compositions to make structural elements such as building blocks, brick, roofing tile, and the like. However, it has been difficult to obtain suitable products since they either lack the strength necessary for structural integrity and/or they cannot be properly cured to the requisite strength under ambient conditions. They must be fired or cured using kilns or other heat processing conditions to obtain the necessary strength or allowed to age for extended periods to achieve the actual degree of cure. The need for fuel to provide the heat and expensive equipment greatly increases the costs, making such structural products economically unavailable. Also, the burning of the fuels again creates a pollution problem. Long term ambient curing requires costly investment in large storage facilities to accommodate accumulating products.
Numerous efforts have been made to overcome this problem including utilization of catalysts in order to increase the rate of strength development of products made from pozzolans. This is disclosed, for example, in U.S. Pat. Nos. 3,990,903 and 4,432,800. In every instance, however, it has not been possible to achieve through hydrothermal reaction at ambient temperatures resultant finished cured cements and building materials which have the necessary high early strength suitable for the mass production of structurally sound structures.
"Hydrothermally cured pozzolanic cement", as that term is used herein, is defined to mean one that is closed cured and achieves its strength by the absorption or consumption of energy (ambient or higher) from its environment, facilitating the conversion of activated or reactive silica-based materials to polyvalent or divalent metal silicates of adhesive or cohesive nature.
It is the cohesive/adhesive or binding properties of the reaction products that provides the structural integrity of hydrothermally cured cements.